Efforts have been made to capture wave energy and transform it into a usable form. Many such efforts attempt to use the kinetic energy of a wave at the surface of the body of water. Such systems generally utilize floating devices which move vertically and/or horizontally with passing waves. This movement is typically transformed into a reciprocating motion to generate a usable form of energy.
An alternative is an "air turbine" type of wave-activated power generation system. In this type of system, an air box is anchored with its upper part above the surface of a body of water having waves. The air box has a lower opening below the surface of the body of water so that an air chamber is formed by the box and the water surface. By repeated vertical displacement of the water surface in the air chamber caused by waves, the air is alternately expelled from and sucked into the air chamber to generate a flow of air which in turn drives an air turbine connected to an electric power generator.
Recently, systems have been disclosed which make use of underwater pressure variations caused by changes in water weight due to the presence or absence of a wave crest above a particular location. U.S. Pat. Nos. 4,203,294, 4,222,238 and 4,630,440 disclose such systems. In particular, U.S. Pat. No. 4,203,294 at FIG. 6, discloses a system including a cylindrical wall member which moves vertically with respect to a fixed cylinder to generate pressurized fluid. However, in this embodiment, the device for generating electrical energy, a turbine, is contained within the apparatus itself. Thus, more than one of these devices could not be hydraulically connected in parallel, to draw unpressurized fluid from a common source and deliver pressurized fluid to a common collection tank.